1. Field of the Invention
This invention relates generally to consumer electronics. More particularly, the invention relates to efficiently storing audio and video data in a memory device.
2. Description of the Related Art
DVD-Audio (DVD-A) is a Digital Versatile Disk (DVD) format that is specifically designed to hold audio data, and particularly, high-quality music. The DVD Forum, consisting of 230 leading companies worldwide, released the final DVD-A specification in March of 1999. The new DVD format is said to provide at least twice the sound quality of audio CD on disks that can contain up to seven times as much information. Various types of DVD-A-compatible DVD players are being manufactured, in addition to the DVD-A players specifically developed for the format.
Almost all of the space on a DVD video disk is devoted to containing video data. As a consequence, the space allotted to audio data, such as a Dolby Digital 5.1 soundtrack, is severely limited. A lossy compression technique—so-called because some of the data is lost—is used to enable audio information to be stored in the available space, both on standard CDs and DVD-Video disks. In addition to using lossless compression methods, DVD-A also provides more complexity of sound by increasing the sampling rate and the frequency range beyond what is possible for the space limitations of CDs and DVD-Video. DVD-Audio is 24-bit, with a sampling rate of 96 kHz; in comparison, DVD-Video soundtrack is 16-bit, with a sampling rate of 48 kHz, and standard audio CD is 16-bit, with a sampling rate of 44.1 kHz.
DVD-Audio allows for a wide variety of audio formats at varying levels of specification. DVD-Audio supports the same multi-channel audio formats used with DVD-Video. Therefore both DVD-Video and DVD-Audio can provide high definition multi-channel audio recorded in the Dolby Digital and DTS audio formats. However, real advantage of the DVD-Audio specification over DVD-Video and CD is in the significantly increased quality of the PCM audio format. PCM or “Pulse-Coded-Modulation” is the audio format standard for CD's and available on many DVD-Video's. DVD-Audio supports a significantly higher quality of PCM audio than is possible on CD or DVD-Video. DVD-Audio PCM can be recorded with a range of frequencies that are more than four times that of a CD while DVD-Audio PCM has a much greater dynamic range that possible on a CD. The greater storage capacity of DVD's allows for much more music to be recorded than possible on CD's.
The following table outlines the technical specifications for PCM on DVD-Audio and standard CD's.
TABLE ISpecificationDVD-AudioCDAudio FormatPCMPCMDisk Capacity4.7 Gb - Single layer650 MB8.5 Gb - Dual Layer17 Gb - Double SidedDual LayerChannelsUp to 62 (stereo)Frequency Response0–96 kHz (max)5–20 kHzDynamic Range144 db96 dbSampling Rate - 244.1, 88.2, 176.4 KHz or44.1 kHzchannel48, 96, 192 KHzSampling Rate -44.1, 88.2, 176.4 KHz orn/amultichannel48, 96 KHzSample Size12, 16, 20, or 24 bits16 bits(Quantization)Maximum Data Rate9.6 MBps.1.4 MBps
In addition to audio, a DVD-Audio disk can contain a limited amount of video, which can be used to display text, such as lyrics or notes; or stills such as a photo album. Such still images, described as Audio Still Video (ASV), are recorded on disc in a separate file. Each still is an MPEG-2 intra-frame and can, optionally, be accompanied by a subpicture for a menu. Still images are pre-loaded into the player's memory before the audio is played or between audio tracks where a mute is acceptable. This allows the images to be presented either as a slide show or browsable by the user. Transitions for still images include cut, fade, dissolve and wipe. Subpictures allow still images to be used as menus or for the display of lyrics etc.
In view of the foregoing, it would advantageous and therefore desirable to provide an efficient scheme for allocating ASV frames in an ASV memory in a DVD audio/video system.